Now Collison, 27, can call himself the youngest self-made billionaire in the world, with a net worth totaling $1.1 billion after Stripe's $9 billion valuation in 2016. The company was designed to transform the way websites accept online payments, and it's a favorite of huge companies like Lyft and Facebook.

Collison started the company with his older brother Patrick, Stripe's CEO. Though the siblings have struck Silicon Valley gold, they haven't forgotten their humble roots in small-town Ireland.

Today, Collison enjoys flying planes, running, and hiking with members of the Stripe team.

Read on to learn more about the world's youngest self-made billionaire.

John was born in Limerick, Ireland, in 1990, and his family eventually settled in the small village of Dromineer.

Before he entered college, Collison had already become a millionaire with his older brother Patrick. They had launched a software firm that made it easier for sellers to manage transactions on eBay.

Collison came to the US to study physics at Harvard in 2009. "It is a weird thing -- people are almost surprised that I'm going to college," he told Ireland's Independent at the time. "There's absolutely no doubt that college is what I want to do."

At first, the brothers rode their bikes to their Palo Alto office every day, in part because they were too cheap to buy a car.

Stripe made its public debut in 2011. The company aimed to simplify the way businesses accepted online transactions by allowing them to integrate payment processing into their websites, instead of forcing users to register and make an account every time.

Stripe.com

By 2015, Stripe was valued at $5 billion, and in November 2016, it spiked to a whopping $9.2 billion. The valuation brought Collison's fortune to $1.1 billion, making him the youngest self-made billionaire in the world at age 26.

He posts pictures on social media of his adventures with fellow Stripe employees, like this trip up Mount Tamalpais in the Bay Area.

Mike Moritz, a Stripe board member, told Bloomberg that the Collisons were more "humble and well-rounded" than your average tech moguls. "There's such an improbability to their story -- that these brothers from a little village would come to build what could well be one of the most important companies on the internet," he said.